Design and Tier-Based Analysis of an Off-Grid Solar PV System for Swarm Rural Electrification in Ethiopia

Abstract

Off-grid photovoltaic systems with battery storage are essential for sustainable rural electrification, yet national programs such as Ethiopia’s NEP 2.0 lack frameworks that support decentralized alternatives. This study introduces a novel swarm electrification model, in which higher-tier solar systems trade surplus energy to support lower-tier households, forming a peer-to-peer solar-sharing network. A comparative assessment of solar resources using models, predictions, and satellite databases showed stable annual irradiance in Ethiopia, ranging from 4.22 to 6.54 kWh/m2/day across two predictive models and two satellite datasets. Long-term PVGIS data (13-year average) recorded the highest annual value at 7.30 kWh/m2/day. Statistically, the artificial neural network yielded the lowest error margins, while the Allen Regression model offered the lowest bias. Based on these data, Tier 2 and Tier 3 PV systems were designed and simulated at 85% efficiency with three-day battery autonomy. A 400 Wp PV array paired with a 2 × 250 Ah battery bank was designed to meet the Tier 3 daily demand of 1.7 kWh, generating over 60% energy surplus. Peak consumption occurs during evening hours (17:00–19:00). Lithium-iron-phosphate batteries proved economically superior for Tier 3 loads exceeding 1.5 kWh/day over a 10–15-year lifecycle, requiring zero replacements and offering lower overall costs. The hierarchical tier-based model enables strategic cross-subsidization, where Tier 3 households support Tier 1 and Tier 2 users. A comparative cable topology analysis recommends the radial T3 2@12V configuration for linear households within 10 m, and the ring T3 topology for longer linear layouts of 15–25 m requiring moderate fault tolerance. All configurations maintain voltage drop below the critical 5% threshold. Overall, this study demonstrates that optimized off-grid PV systems with appropriate topology and battery selection offer a sustainable and scalable pathway for rural electrification in Ethiopia.